You're welcome, pukie!
You play custom balls, and these wear and tear (and get lost BTW).
In the low right corner of the game client, right from the ball, there is a ruler showing how much "life" your ball has. If it's over, it is taken out of the game.
The durability (sp?) is a feature of the balls, shown in the Pro Shop.
Since the custom balls are much better than the Starters w/ unlimited life, I accept this as a small green fee (mine are about 6 cr / 9 holes).